The present invention is directed to semiconductor packaging, and, more particularly, to a method of assembling a semiconductor device including a semiconductor die with an insulating substrate and a heat sink.
Semiconductor device packaging fulfils basic functions such as providing electric connections and protecting the die against mechanical and environmental stresses. The completed semiconductor device may be mounted on a support with electrical connectors, such as a printed circuit board (‘PCB’), for example. The semiconductor device may have exposed external electrical contact surfaces or leads for connection to the electrical connectors on the support. Using surface mount technology, external electrical contact surfaces or leads of the package can be soldered directly to corresponding pads on the support, providing mechanical attachment as well as electrical connections.
Semiconductor devices are commonly packaged for surface mounting by encapsulating one or more semiconductor dies, the encapsulation process including embedding the die or dies in a molding compound. Various techniques are available for connecting the external electrical contact surfaces or leads of the package internally with electrical contact pads on the embedded semiconductor die.
In a wire bonded package, the die may be mounted on a die support with the contact pads of the die on its active face opposite from the die support. Wires may then be bonded to the contact pads and to the external electrical contact surfaces or leads of the package to provide the internal connections, before encapsulation.
In a lead frame type package, the die support may be an electrically conductive lead frame, whose frame members are cut off and discarded during production, to isolate the electrical contact surfaces or leads of the package from each other, after applying molding compound to encapsulate the die, the internal connections and the external electrical contacts from the lead frame. With this technique, the external electrical contacts of the package may be disposed around the periphery of the semiconductor die, either in an active face of the finished device or at edges of the device. However, the minimal pitch and the numerical density of the external electrical contacts is limited by the risk of short circuits between adjacent contacts.
In an insulating substrate package, such as a laminate base package or ceramic base package, the die may be mounted on an electrically insulating substrate bearing the external electrical contact surfaces. Examples of laminate base packages include ball grid array (BGA), pin grid array (PGA) and land grid array (LGA) packages. In one technique of insulating substrate packages, before encapsulation, internal connections are made by wire bonding between the contact pads of the die and the external electrical contact surfaces. After encapsulation, an array of solder balls or studs may be applied to the external electrical contact surfaces, typically before singulation of the encapsulated devices. In place of the balls or pins, LGA packages have metal pads, of bare gold-plated copper for example, that are contacted in use by pins on a mother board.
Such insulating substrate packages enable a smaller pitch and a higher numerical density of the external electrical contacts. However, typically the electrically insulating substrate is also thermally insulating. For certain types of semiconductor devices, such as high power devices for example, it is desirable to mount the semiconductor die or dies on a heat sink element, such as a metal or other thermally conductive flag, distributing internally generated heat over the face of the semiconductor die or dies and dissipating the heat, by conduction radiation and/or convection.
It is desirable that provision of a heat sink in an insulating substrate semiconductor die package should minimize complication of the packaging process and not increase costs.